Clone a TTree into a separate file

ROOT
1

When I am trying to copy a file to a different file, I end up getting an error that looks like this :


Error in <TFile::ReadBuffer>: error reading all requested bytes from file newFile.root, got 0 of 28863
Error in <TFile::ReadBuffer>: error reading all requested bytes from file newFile.root, got 0 of 28863
terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

My attempt at copying a tree to a different file

    TFile *if = new TFile("somefile.root");

    TTree *tr = (TTree*)inf->Get("QCDAna/tree2");

    TFile *of = new TFile("newFile.root", "recreate");
    of->cd();
    tr->Write("blah");
    of->Close();
    if->Close();
2

Try

    TFile *if = new TFile("somefile.root");

    TTree *tr = (TTree*)inf->Get("QCDAna/tree2");

    TFile *of = new TFile("newFile.root", "recreate");
     tr->CloneTree(-1,"fast");

    of->Write();
    delete of; 
    delete if;
3

You also seem to have a typo in your example, it should be:

TFile *if = new TFile("somefile.root");
TTree *tr = (TTree*)iff->Get("QCDAna/tree2");

(if, not inf in the Get call).

4

“if” is probably quite a bad variable name, in many programming languages :slight_smile:

5

@Graipher, obviously a bad choice, :grin:
thanks for pointing out

@pcanal, do I have to also do
tr->CloneTree(-1,"fast")->Write();

The command you gave worked, but nothing shows up as copied. But, if I chain it with Write, it worked !

6

Indeed I was missing a call to Write in my code snippet (I update my post).

You can indeed either call Write on the TTree or the TFile in this case.

Cheers,
Philippe.